1. Field of the Invention
The present invention relates generally to testing of a communications network, and more specifically to equipment and method for testing ATM (asynchronous transfer mode) switches and networks.
2. Description of the Related Art
In the asynchronous transfer mode, digital signals are segmented into blocks called “cells” of fixed length and each cell is transmitted with a header containing source and destination addresses and cell type information and so forth. ATM transmission systems are tested in a number of aspects including the inter-node connectivity between nodes (or ATM switches), the intra-node connectivity, the transmission quality, the one-way transit (propagation delay) times and round-trip transit time between nodes in order to assess the cell delay variation of the ATM transmission system. The frame timing difference between nodes is another measurement item to be tested.
It is the usual practice for ATM maintenance routines to provide out-of-service measurement by isolating lines and equipment from working facilities before they are subjected to measurement. For in-service measurement, the ITU-T Recommendation I.610 states that information flows F4 and F5 be used respectively at the virtual path and virtual channel planes across ATM nodes. However, complex circuitry would be required for implementing a test on ATM networks at the level of virtual channel with the F5 flow information. Hence, the VC level testing is not Gently supported.
Therefore, in-service connectivity test is currently performed on an end-to-end basis and in-service propagation delay time measurements are currently conducted by network nodes.